Numerous stent designs are known in the art, of which self-expanding and balloon-expandable stents are the predominant commercially available types. Self-expanding stents, such as described in Gianturco U.S. Pat. No. 4,580,568, generally provide good crush-resistance and axially flexibility, thus permitting delivery through tortuous anatomy, but provide lower radial strength once deployed. Balloon-expandable stents, such as typified by Palmaz U.S. Pat. No. 4,739,762, provide high radial strength, but tend to have increased axial rigidity that affects deliverability through tortuous vessels. It has therefore been a goal of many balloon expandable stent designs to enhance axial flexibility of the stent to improve deliverability, and thus the number of potential applications for the device.
Previously known stents generally are provided in a variety of lengths and diameters, so the clinician can select the stent most appropriate for a specific patient. Such stents typically have homogeneous properties along the length of the stent, and provide limited options for customization responsive to the needs of a particular patient.
There may be applications, however, where the best solution for a particular patient would involve a combination of the features of both balloon-expandable and self-expanding stents. It would therefore be desirable to provide a modular stent that permits the clinician to “mix and match” stent modules to build a stent having specific characteristics tailored for a specific patient or application.
For example, it may be desirable to provide a stent having axial modules of variable rigidity and crush-resistance, such as for use in the carotid arteries. Due to the generally exposed nature of these arteries in the region of the neck, situations have been reported where balloon-expandable stents have been subjected to partial crushing. On the other hand, self-expanding stents are susceptible to migration. It therefore may be desirable in certain applications to provide a stent having a resilient central portion and balloon-expandable end regions that permit the stent to be anchored in position.
The ability to vary the mechanical properties of the stent also would permit a stent to include non-metallic components, such as biodegradable or bioabsorbable segments. This ability might prove particularly advantageous where it is desired to deliver a predetermined dose of drug to via drug-eluting segments, for example, by incorporating a specified number of drug-eluting segments into the prosthesis.
As yet another example, U.S. Pat. No. 6,048,361 to Von Oepen describes a stent designed for use in bifurcated vessels having a side branch aperture. As described in that patent, the stent is manufactured with fixed length regions proximal and distal to the aperture. Thus, the stent may not be suitable in some patients because the fixed length of the proximal or distal region may interfere with collateral vessels upstream or downstream of the bifurcation. Accordingly it would be desirable to provide a vascular prosthesis that includes a side branch aperture, but which has proximal and distal regions that may be tailored for a specific patient.
U.S. Pat. No. 5,824,037 to Fogarty et al. describes a modular intraluminal prosthesis, such as for a stent-graft, comprising a plurality of modules having standard interface ends for engaging adjacent modules. The modules employed in the prosthesis may include variations in axial length, cross-section, perimeter, resilient expansive force and axial flexibility. The modules are “locked” together using stitching in combination with the liner material.
One drawback of the prosthesis described in the Fogarty et al. patent is that the prosthesis may lack structural rigidity in the expanded configuration. In particular, the patent describes no mechanism to positively engage the modules other than the liner material. It therefore would be desirable to provide a modular stent wherein the modules cannot be locked together without stitching or a liner material.
The foregoing patent also does not suggest that a modular stent may be used to improve conformance of the stent to a patient's vasculature when used in a bifurcated region, or the desirability of intermixing segments comprising different materials, including bioabsorbable or drug-eluting segments.
It therefore would be desirable to provide a vascular prosthesis comprising a plurality of modular segments interconnected by lockable joints that enhance articulation between adjacent segments during delivery of the prosthesis and enhance structural rigidity of the prosthesis in the deployed configuration.
It also would be desirable to provide a vascular prosthesis comprising a plurality of modular segments interconnected by a plurality of joints wherein the modular segments comprise different materials or strut configurations, thereby permitting the structural rigidity of the vascular prosthesis in the deployed configuration to be tailored for a specific patient or application.
It further would be desirable to provide a vascular prosthesis comprising a plurality of modular segments, wherein one or more segments may be bioabsorbable or drug-eluting, to provide predetermined doses of drug to the vessel wall or intravascularly to a desired tissue region.
It still further would be desirable to provide a vascular prosthesis comprising a plurality of modular segments, wherein one or more segments may be intermixed to provide a desired feature having proximal and distal regions of customizable length, for example for treatment of bifurcated vessels or aneurysms